ATHENS — Days before his emphatic victory in the Greek elections, Alexis Tsipras appeared at
the final campaign rally of his left-wing Syriza party with a ponytailed
Spaniard named Pablo Iglesias, whose own far-left political movement is now
shaking up Spain.

The two men embraced like fellow insurgents, as speakers
blasted the edgy lyrics of Leonard Cohen: “First we take Manhattan, then we
take Berlin.”

“The wind of democratic change is blowing in Europe,” Mr.
Iglesias, leader of the Podemos party in Spain, declared in Greek to a
flag-waving throng of Syriza supporters. “Change in Greece is called
Syriza. And change in Spain is called Podemos. Hope is on the way.”

No doubt Berlin is paying close attention, and Brussels,
too. The rise of Syriza is a challenge to Europe’s German-led economic policies
of austerity, and Mr. Tsipras has vowed to renegotiate the

But it is
also a pointed threat to the European political status quo, as a new generation
of leaders — including Prime Minister Matteo Renzi of Italy — emerges
and anti-establishment parties on the right and left gather strength.

Indeed, many anti-establishment leaders on the far right —
including Marine Le Pen of the National Front in France and Nigel Farage of the
U.K. Independence Party in Britain — embraced Syriza’s victory as a triumph
against European elites.

If this
reflected a healthy dose of political opportunism, the support from the far
right also underscored how the anti-austerity movement provided a huge tent in
which political lines were easily blurred. To form a government, Mr. Tsipras
on Monday allied with a small center-right party, Independent Greeks.

“Make no mistake, it is a huge ideological compromise,” Nick
Malkoutzis, a political analyst in Athens, said. But, he added, “they
have similar positions on how to approach the bailout. So although they
disagree on everything else, this is the key to Syriza’s being right now.”

The Syriza
victory comes as Germany’s
dominance over European decision-making seems to be weakening, if only
slightly. Despite the reported unhappiness of Chancellor Angela Merkel
of Germany, the European Central Bank last week announced a trillion-euro program to buy government bonds in
hopes of staving off deflation and stirring economic growth.

At the same time, leaders in France and Italy have been
demanding for months that the budgetary constraints of austerity be eased.

Now much
attention will be focused on Mr. Tsipras, who was sworn in Monday as the new
prime minister of Greece.
Throughout the campaign, opponents depicted him as an inexperienced
radical whose demand to renegotiate the bailout terms could backfire and wreck
the country. Mr. Tsipras confronted that criticism directly in his acceptance
speech on Sunday night, when he declared that his party would prove that it
could govern responsibly and well.

“The new
Greek government will convince people that this is not a catastrophe for the
country,” he said. “Catastrophe is not imminent.”

If so, many analysts say other upstart European parties will
be beneficiaries. “It will make clear that these parties can come to power
without destroying the country,” said Manuel Arias Maldonado, a professor of
politics at Malaga University in Spain. “We are paying a lot of attention to
Greece.”

In Spain, the
emergence of Podemos has been swift and unexpected. Founded early last
year, Podemos won almost 8 percent of the Spanish vote in European parliamentary elections last May —
which denied the governing conservative Popular Party and the opposition
Socialists a majority of votes for the first time since Spain’s return to
democracy in the late 1970s.

Polls show
that Podemos continues to gain ground as national elections approach — they are
expected around November — and party leaders are hurriedly trying to build a
nationwide political organization.

Like
Syriza, Podemos has pushed an anti-austerity message and called for debt
renegotiations with creditors, while Spain’s traditional parties have
echoed their Greek counterparts by warning that Podemos is a threat to the
country’s tentative economic recovery.

Mr.
Iglesias, a college lecturer, has been attacking the Socialists and arguing
that only Podemos can provide a true alternative to the conservative Popular
Party.

“It is clear that now there
is a rift on the European question, between euroskeptics, whether they are on
the left or the right, and those who believe that Europe needs to continue its
political and economic construction,” said Pascal Perrineau, a professor at the
Institut d’Études Politiques in Paris.
“This rift has nothing to do with the left-right split,” he
added. “That is why both Ms. Le Pen and the left-of-the-left are delighted by
what happened in Greece.”

This
broader political trend might explain why Ms. Merkel has praised Mr. Renzi and
worked to develop a rapport with him, even as the Italian prime minister has
regularly spoken out against austerity policies and gleefully praised the
stimulus plan of Mario Draghi, the head of the European Central Bank.

Mr. Renzi
remains popular with Italian voters and has positioned himself as a rebel
inside the system, as he pushes his left-wing Democratic Party further to the
right — while challenging the European Union to allow Italy more flexibility in meeting
budgetary requirements.

Mr. Renzi
and Mr. Tsipras have apparently never met, and the men, both 40, have their
differences. Yet if Mr. Renzi has not endorsed a renegotiation of
bailout agreements, whether for Italy or any other country, analysts say he
will inevitably benefit from the hard-line push against austerity by Mr.
Tsipras in Greece, and from the effort by Podemos in Spain.

“Renzi
believes that European policy of fiscal austerity is excessive and wrong, which
is similar to Tsipras,” said Guido Tabellini, a professor of economics at BocconiUniversity
in Milan. “But
that is about it. Their economic policies don’t have much more in common.”

In Italy, the main anti-establishment party has been the
Five Star Movement, led by the comedian Beppe Grillo. But Mr. Grillo has seen his
popularity dip as Mr. Renzi has steadily become the central figure in Italian
politics. Mr. Renzi’s relationship with Mr. Tsipras will be closely watched.

“Tsipras might help Renzi to convince the E.U. to have
fiscal policy less obsessed with balanced budget constraints,” Mr. Tabellini
said, “while Italy can push Greece to start and boost reforms.”

Mr. Tsipras needs no reminder that he is unloved by the
Greek political establishment that he thrashed. In a break with custom, the
departing prime minister, Antonis Samaras of the conservative New Democracy
Party, did not attend the swearing-in ceremony for his successor.

According to a Syriza official, Mr. Tsipras found his prime
ministerial office completely bare — with the safe open and empty. A political
jab, no doubt, but also a reminder of the challenges ahead.